Thermotropic liquid crystalline polymers (LCPs) made from a partially aromatic polyester such as poly(ethylene terephthalate) (PET), and one or more aromatic hydroxy-carboxylic acids such a p-hydroxybenzoic acid (HBA) are well known, see for instance U.S. Pat. Nos. 3,778,410 and 3,804,805.
Though U.S. Pat. No. 4,892,912 discloses the preparation of LCPs from a partially aromatic polyester, an acyloxyaromatic carboxylic acid, and a diacyloxyaromatic compound, it does not disclose use of carboxylic acid anhydrides.
U R URINOV et al., Vysokolekulyamye Soedineniya, Ser. B, vol. 37, (1995), pp. 262-230 describes the synthesis of LCPs from partially aromatic polyester, acetoxybenzoic acid, and diacetoxyhydroquinone in the presence of acetic acid. It does not disclose the use of carboxylic acid anhydrides.
U.S. Pat. No. 5,326,848 discloses an LCP with repeat units derived from ethylene glycol (EG), 6-hydroxy-2-naphthoic acid (HNA), p-hydroxybenzoic acid (HBA), and terephthalic acid (T). It does not disclose or suggest using a stoichiometric excess of any ingredient.
Conventional (non-LCP) copolyester resins are known that provide low melt processing temperatures, isotropic properties, and good optical properties. This class of copolyester incorporates aliphatic moieties and alicyclics and consequently they exhibit high permeation properties (>160 cm3 oxygen 25 μm/m2 day atm).
Conventional LCP polyesters are known to provide good oxygen barrier properties, but they tend to be anisotropic and therefore weak in the direction transverse to melt flow, they have low elongation-to-break, and they tend to be opaque.
It would be beneficial to have an LCP barrier resin having good barrier properties, being processible at lower melt temperatures, having good optical properties or clarity for packaging applications.